my fish are dying!

This is a discussion on my fish are dying! within the Tropical Fish Diseases forums, part of the Freshwater Fish and Aquariums category; -->
I recently got some Platies and I didn't quarantine (I know- I should have) and 3 of them died within 2 weeks. So I ...

I recently got some Platies and I didn't quarantine (I know- I should have) and 3 of them died within 2 weeks. So I was worried that they had a disease from the store but all of my other fish were ok. But today I found 3 of my serpae tetra dead and 2 of my zebra danios. Now I'm afraid that they spread a disease. The fish didn't look sick that I noticed. I would just find them dead in the tank. I have 10 serpae tetras, 2 Platies are left, 4 zebra danios, 2 Otos (I'm going to get more. I bought 4 and one was DOA and I lost the other one when I redid my tank), 3 amano shrimp, and 5 leopard cories (I just realized I'm kind of attached to those) so now I'm scared all of my fish are going to start dying. Is there a medicine I can use to dose the tank that will kill whatever disease is in there?
My tank is 55 gallons, and the water parameters are normal.
HELP!

ETA: I'm pretty sure one of my serpae tetras is in the process of dying right now. Its mouth is wide open and it looks like its stomach is slightly swollen.

I recently got some Platies and I didn't quarantine (I know- I should have) and 3 of them died within 2 weeks. So I was worried that they had a disease from the store but all of my other fish were ok. But today I found 3 of my serpae tetra dead and 2 of my zebra danios. Now I'm afraid that they spread a disease. The fish didn't look sick that I noticed. I would just find them dead in the tank. I have 10 serpae tetras, 2 Platies are left, 4 zebra danios, 2 Otos (I'm going to get more. I bought 4 and one was DOA and I lost the other one when I redid my tank), 3 amano shrimp, and 5 leopard cories (I just realized I'm kind of attached to those) so now I'm scared all of my fish are going to start dying. Is there a medicine I can use to dose the tank that will kill whatever disease is in there?
My tank is 55 gallons, and the water parameters are normal.
HELP!

ETA: I'm pretty sure one of my serpae tetras is in the process of dying right now. Its mouth is wide open and it looks like its stomach is slightly swollen.

This sucks

Do the standard stuff, test the water, look for parasites, and signs of illness.
something is killing them

Is there anything unusual? Fuzzy growths? Turning black or any other colour before dying? Is this the only one that seems bloated? I don't know much about diseases I'm afraid... or meds but the more info you can give us the better.

FYI, we all do it, we've all done it, not everyone has the money for extra tanks for QT. Have you also tested your water and parameters? Done a water change lately?

Rickey- that fish that I said was in the process of dying just died. Like I said, the only symptoms it had was that its mouth was wide open and its stomach looked slightly swollen and its color was slightly faded. It was swimming weird- kind of staying in the same area and moving in a twitchy way and then started tipping over near the top and then I found it stuck to the filter intake about 10 minutes later. All of the other ones that died have just been shown up dead. I never saw any of them with symptoms. And like I said, I checked my water parameters and they are normal.

SeaHorse- all the ones I've found dead just have faded color and the one that I saw die a few minutes ago was only faded and had its mouth open. I didn't notice any other symptoms besides the way it was swimming.
I redid my tank about a month ago and I haven't done a water change yet. I've just been topping it off a lot because the water evaporates very rapidly.
And like I said above, the water parameters are normal.

All that i would do if i was in your situation is to try to check your fish regularly looking out for some of the more common diseases. You should also try to do a water change water quality or a spike in a chemical could be killing them since you see no signs of disease. I would highly recommend taking out the fish that look sick and quarantine them, treat them with methylene blue just in case and hopefully every thing turns out well. When i was still new to fish keeping i went out and bout loads of fish like 20 guppies 7 goldfish and the majority of them died of ich. It sucked but by the time i figured out what was going on it was too late. Anyway goodluck

SeaHorse- all the ones I've found dead just have faded color and the one that I saw die a few minutes ago was only faded and had its mouth open. I didn't notice any other symptoms besides the way it was swimming.
I redid my tank about a month ago and I haven't done a water change yet. I've just been topping it off a lot because the water evaporates very rapidly.
And like I said above, the water parameters are normal.

When you say you "redid your tank" what exactly did that mean? Just rearrange your decorations? or emptied and scrubbed it out? Is it possible you caused a Ammonia spike with the tank changes and the new fish being added? Rather than "normal" can you give us the numbers? We're just trying to help sort this out with you.